This project is investigating the size and spatial distribution of cortical "colonies" that are associated with individual muscles, as well as the function of neurons in such colonies in the motor cortex and supplementary motor area during voluntary motor behavior. Also under investigation is the possible gating of sensory input to neurons in the motor-sensory cortex of cats. Intracortical microstimulation can activate a forearm muscle over a wide region of cortex and possibly form multiple isolated regions. Excitation or inhibition of the same muscle can be produced from closely space positions in the cortex. Long-term chronic recording from the same neuron has now reached 109 days. During this period the relationship between the cell discharge properties and the "best" movements appears to be stable.